/*
 * Copyright 2017 Huawei Technologies Co., Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.servicecomb.foundation.vertx.server;

import java.io.UnsupportedEncodingException;

import io.netty.buffer.ByteBuf;
import io.vertx.core.Handler;
import io.vertx.core.buffer.Buffer;
import io.vertx.core.parsetools.RecordParser;
import io.vertx.core.parsetools.impl.RecordParserImpl;

/**
 * TcpParser
 *
 *
 */
public class TcpParser implements Handler<Buffer> {
    public static final byte[] TCP_MAGIC;

    public static final int TCP_HEADER_LENGTH = 23;
    static {
        try {
            TCP_MAGIC = "CSE.TCP".getBytes("UTF-8");
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    enum ParseStatus {
        TCP_HEADER,
        TCP_PAYLOAD
    }

    private TcpBufferHandler outputHandler;

    private RecordParser parser;

    private ParseStatus status;

    private long msgId;

    // 仅仅是header + body，不包括headerLen本身
    private int totalLen;

    private int headerLen;

    public TcpParser(TcpBufferHandler output) {
        this.outputHandler = output;

        reset();
    }

    /**
     * 在解析出错时，通过重新创建parser对象，将整个缓冲区重置
     */
    protected void reset() {
        parser = RecordParserImpl.newFixed(TCP_HEADER_LENGTH, this::onParse);
        status = ParseStatus.TCP_HEADER;

        parser.handle(Buffer.buffer(0));
    }

    public boolean firstNEqual(byte[] a, byte[] b, int n) {
        assert a.length >= n && b.length >= n;

        for (int i = 0; i < n; i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }

    protected void onParse(Buffer buffer) {
        switch (status) {
            case TCP_HEADER:
                ByteBuf buf = buffer.getByteBuf();
                if (!firstNEqual(TCP_MAGIC, buf.array(), TCP_MAGIC.length)) {
                    reset();
                    return;
                }

                buf.skipBytes(TCP_MAGIC.length);
                msgId = buf.readLong();
                totalLen = buf.readInt();
                headerLen = buf.readInt();

                if (totalLen == 0) {
                    onReadOnePackage(null, null);
                    return;
                }

                parser.fixedSizeMode(totalLen);
                status = ParseStatus.TCP_PAYLOAD;
                break;

            case TCP_PAYLOAD:
                Buffer headerBuffer = buffer.slice(0, headerLen);
                Buffer bodyBuffer = buffer.slice(headerLen, buffer.length());
                onReadOnePackage(headerBuffer, bodyBuffer);
                break;

            default:
                break;
        }
    }

    private void onReadOnePackage(Buffer headerBuffer, Buffer bodyBuffer) {
        outputHandler.handle(msgId, headerBuffer, bodyBuffer);

        parser.fixedSizeMode(TCP_HEADER_LENGTH);
        status = ParseStatus.TCP_HEADER;
    }

    public void handle(Buffer buf) {
        parser.handle(buf);
    }
}
